Variables

Variables are used to store and manipulate data within shell scripts.

# Using variables
name="ram"
age=30
echo "Hello, $name! You are $age years old."

Scalar Variables:

# Scalar variables hold single values, such as integers, strings, or floating-point numbers.
name="ram"
age=30
pi=3.1415

Array Variables:

#Array variables can hold multiple values, typically indexed by integers.
fruits=("apple" "banana" "orange")
numbers=(1 2 3 4 5)

Environment Variables:

# These are global variables that are predefined in the shell environment. They are accessible to all processes.
HOME=/home/user
PATH=/usr/local/bin:/usr/bin:/bin

Local Variables:

# Local variables are defined within a specific shell script or function and are not accessible from outside that context.
# Inside a function
local localVar="This is a local variable"

Special variables

$0      # The name of the script or shell
$1, $2  # The first and second command-line arguments
$$      # The process ID of the script
$?      # The exit status of the last command

Read-Only Variables:

# Some variables, like UID or SHELL, are read-only and cannot be modified by the script.

readonly UID
readonly SHELL

for loop

for item in list
do
  # Commands to be executed for each item
done

sample:1

#!/bin/bash

# Define a list of numbers
numbers="1 2 3 4 5"

# Use a for loop to iterate over the list
for num in $numbers
do
  echo "Number: $num"
done

sample:3

#!/bin/bash

# Use command substitution to generate a list of filenames in the current directory
for file in $(ls)
do
  echo "File: $file"
done

while loop

#!/bin/bash
# A more advanced Bash shell script example

# Variables
count=1

# Looping with while
while [ $count -le 5 ]; do
  echo "Iteration $count"
  count=$((count + 1))
done

case

#!/bin/bash

# Case statement
read -p "Enter a fruit (apple, banana, or orange): " fruit

case $fruit in
  "apple")
    echo "You chose an apple."
    ;;
  "banana")
    echo "You chose a banana."
    ;;
  "orange")
    echo "You chose an orange."
    ;;
  *)
    echo "Invalid choice."
    ;;
esac

# Function definition
greet() {
  echo "Hello, $1!"
}

# Function call
greet "Alice"

operators in shell scripting:

• -eq: Equal to
• -ne: Not equal to
• -lt: Less than
• -gt: Greater than
• -ge: Greater than or equal to

In shell scripting, if statements are used to make decisions based on the evaluation of a condition. Here are some if condition examples in Bash, a common Unix-like shell:

Basic if Statement:

Copy code
#!/bin/bash

# Check if a number is greater than 10
number=15

if [ $number -gt 10 ]; then
  echo "$number is greater than 10."
fi
if-else Statement:

#!/bin/bash

# Check if a number is even or odd
number=7

if [ $((number % 2)) -eq 0 ]; then
  echo "$number is even."
else
  echo "$number is odd."
fi

if-elif-else Statement:

#!/bin/bash

# Check if a number is positive, negative, or zero
number=-5

if [ $number -gt 0 ]; then
  echo "$number is positive."
elif [ $number -lt 0 ]; then
  echo "$number is negative."
else
  echo "$number is zero."
fi